Macrophages and monocytes have been shown to inhibit tumor growth both in vivo and in vitro. Neoplasias, however, may subvert the function of these cells by the release of soluble immunosuppressive factors and such factors have indeed been found in humans with cancer and in tumor-bearing mice. We have previously characterized a factor which suppresses macrophage function from the tumors, plasma, and urine of mice bearing transplanted or spontaneous carcinomas and from extracts of certain oncogenic murine viruses. We have shown that the suppressive factor(s) for macrophages is physiochemically and antigenically related to retroviral P15E. Interestingly, human cancerous effusions also contain a factor(s) which inhibits normal monocyte function and is antigenically related to P15E. We will now use several different immunological procedures to examine the tumors, serum and urine of mice bearing transplanted, spontaneous, or chemically-induced tumors for the presence of proteins related to P15E. The procedures which will be used include: (1) radioimmunoassay using monoclonal antibodies to P15E coupled to a solid-phase support such as sepharose; (2) affinity chromatography, using monoclonal alphaP15E coupled to sepharose, of large sample volumes followed by elution and SDS-PAGE of bound materials. The electrophoresed proteins will then be electro-blottted to derivatized paper followed by incubation with monoclonal AlphaP15E and then incubation with 125I-labeled goat Alphaamouse IgG; (3) metabolic labeling of tumor cells with 35S-methionine followed by immunoprecipitation using monoclonal AlphaP15E. In addition to verifying the association of P15E-related proteins with various tumors we will correlate the levels of such proteins with the rate and presence of tumor growth and the metastatic potential of the tumors. We will also use the monoclonal antibodies to P15E as an immunotherapeutic approach to control tumor growth in mice receiving transplanted tumors or as passive immunization for mice exposed to chemical carcinogens. The development of sensitive means for detecting this immunosuppressive factor(s) in tumor-bearing mice will allow the future development of such immunoassays in humans where a P15E-related protein has also been implicated in immunosuppression. The early detection of such immunosuppressive factors may allow treatment at a stage when these factors exert their greatest effect.